ただ details

write + merely

tada kaku dake da

merely; nothing but — the thing is no more than what it is, and the speaker says so on purpose

meaning: do nothing but write

今いまできることはもうない。ただ待つまつだけだ。

ima dekiru koto wa mou nai. tada matsu dake da.

There is nothing more we can do now. We do nothing but wait. neutral

文句もんくを言いいたいわけじゃなくて、ただ確認かくにんしたいだけなんだ。

monku o iitai wake ja nakute, tada kakunin shitai dake na n da.

I'm not trying to complain, I just want to check, that's all. casual

Examples

nothing but; merely — the act or the thing is presented as small, and that smallness is the point

今いまできることはもうない。ただ待まつだけだ。

ima dekiru koto wa mou nai. tadamatsudakeda.

There is nothing more we can do now. We do nothing but wait. neutral

文句もんくを言いいたいわけじゃなくて、ただ確認かくにんしたいだけなんだ。

monku o iitai wake ja nakute, tada kakunin shitai dake na n da.

I'm not trying to complain, I just want to check, that's all. casual

当方とうほうといたしましては、ただ事実じじつをお伝つたえするだけでございます。

touhou to itashimashite wa, tada jijitsu o o tsutae suru dake de gozaimasu.

For our part, we are merely conveying the facts. formal

only a; a mere — before a noun, the thing is no more than the ordinary case of it

心配しんぱいしなくていいよ。ただの風邪かぜだから。

shinpai shinakute ii yo. tada no kaze da kara.

No need to worry, it's only a cold. casual

あれはただの噂うわさで、根拠こんきょは何なにもない。

are wa tada no uwasa de, konkyo wa nani mo nai.

That is nothing but a rumour, with no basis at all. neutral

Sentence-initial ただ is a different word — a conjunction meaning "except
that": 面白おもしろい。ただ、少すこし長ながい。

だけ
だけ draws the boundary and can be perfectly neutral about it; ただ in front declares the amount inside small, which is why ただ見みているだけだ makes an excuse and 見みているだけだ merely reports what someone is doing.
のみ
のみ is the written restrictor and needs no adverb propping it up; ただ〜だけ tends to the spoken end, so a notice writes 関係者かんけいしゃのみ where the same point in conversation usually comes out as ただ〜だけ.
しか〜ない
しか〜ない counts what is left and calls it too little; ただ〜だけ counts the same amount and calls it unimportant — 一ひとつしかない complains about the shortage, ただ一ひとつだけだ says the one is all it ever was.

ただし
ただし fences off an exception to what was just said (ただし、雨天うてんは中止ちゅうし); this ただ measures an amount instead, so it qualifies nothing that came before it and needs no previous sentence to attach to.